Photochemical preparation of gamma benzene hexachloride



Patented Nov. 14, 1950 PHOTGCHEMICAL PREPARATION OF 'y BENZENEHEXACHLORIDE Max Gonzo, Forest-Brussels, Belgium, assignor to Solvay &Cie, Brussels, Belgium, a Belgian Company Application August 23, 1946,Serial No. 692,72fi in Belgium September 24, 1945 8 Claims.

It is known that both the a and the B isomers of benzene hexachloridecan be obtained by causing a current of chlorine gas to bubble throughbenzene under sun light. Moreover, by operating in presence of a dilutesolution of caustic soda Vanderlinden, (Bericht 1912) was able toisolate next to the a and p isomers two new isomers of benzenehexachloride melting at 112 C. and 129 C. respectively, which isomerswere named 'y and a respectively.

More recently the Great Western Electrochemical Company (U. S. PatentNo. 2,010,841) was able to obtain a mixture of the four isomers byintroducing benzene into liquid chlorine in the absence of light and ofa catalyst. Lastly Socit Progil (Belgian Patents No. 456,066 and456,561) has obtained in divided form benzene hexachloride of relativelylow melting point (120) and.

relatively soluble in benzene, by chlorinating benzene either inpresence of a catalyst which does not convey chlorine, such as mercury,or in presence of an oxidising catalyst (nitrogen oxide) or again inpresence of water or of a concentrated 'less soluble in benzene than theothers and, in

accordance with this invention, advantage is taken of that property bycarrying out the chlorination'under such conditions that crystals of thea and p isomer are separated from the solution, preferably as soon asthey are formed, so that the chlorination can be continued until thesolution is practicall saturated with 'y isomer.

The reaction is eflected .at atmospheric temperature in an enclosurelighted with artificial light and the chlorination is interrupted only.when the benzenic solution of benzene hexachloride is saturated orpractically saturated with 'y isomer so that a solution is'obtained thatis very rich in isomers other than a and 19.

I have ascertained the surprising fact that after evaporating thatsolution the resulting solid prodnot has a melting point of the order of70 0.,

which temperature is considerably lower the that of the compounds ormixtures obtain: hitherto (above 112 6.) and furthermore tl said productis very soluble in the usual solvent The crystals of the a and ,8isomers separate in the course of chlorination are washed wil benzene inorder to recover the impregnatir mother liquor and the liquor washedaway, are having been enriched with benzene if desired, used as startingmaterial fo a fresh chlorim tion.

Further features of the invention relate to tl steps for convenientlycarrying out the abo" process. Thus, in Order to attain easily the sauration with 'y isomer it is advisable to reduc or better to avoid, theformation of crystals of t1 0. and p isomers within the chlorinationvat. this end, an advantageous method consists i continuously drawingoff the reacting solutio cooling it to cause the a and ,9 isomers tocrysta lize, separating said isomers by centrifuging orl any other knownprocess and then reintroducii into the chlorination vat the solutionfreed fro: crystals. This method of operation has the ar vantage ofavoiding stoppages in the chlorine fer pipe, of maintaining efficaciouslighting of ti solution, which would not be the case if the s lutionheld many crystals in suspension, and 1 facilitating adjustment of thetemperature l avoiding the formation of crhsts whichwou form aheat-insulating layer on the wall of ti receptacle.

Figs. 1 and 2 of the drawin illustrate diagran matically, by way ofexample, arrangement 1 apparatus which are suitable respectively for tlcontinuous and the discontinuous operation 1 the process according tothis invention.

For continuous operation, into the chlorlnatic receptacle A containing asolution at a concez tration corresponding to saturation with each i theisomers a, p and 'y at the temperature of ti crystalllzer, I introducebenzene and chlorine such proportions that the solution remains pra1tlcally saturated with isomer y at the temper: ture considered. At B Icontinuously withdra a fraction of the saturated solution which cooledin a crystall zer R, the crystals formed a:

filtered in a suitable apparatus F and a portic of the solution isreintroduced at C into the ch11 'dried, gives about 900 cycle at 81 ased product. The crystals withdrawn at F are washed with benzene in ascrubbing tower L and the resulting solution is reintroduced at D intothe chlorination vat A. In order to keep the process continuous, itsuflices to withdraw at S! and S: quantities of benzenic so'lution andof crystals corresponding to the amounts of raw products used.

The benzenic solution rich in isomers other than a and p which isobtained by the process according to this invention may be used such asit is. or in emulsion form, as an insecticide. It

' tion of y benzene hexachloride in benzene, commay also be subjected toevaporation with water vapour or to any other suitable treatment inorder to separate therefrom the benzene, the chlorobenzenes (i. e.substitution products which are not combined with the chlorine byaddition in the chlorination vat) and a mixture of henzene hexachloridesof very low melting point (under 70 0.) very soluble in the usualsolvents.

In that case the benzene is sent back to the chlorination step and thecrystalline product is used as an insecticide, either as it is, or inadmixture with diluents.

Example (Fig. 2)

I introduce 1 kg. of benzene into a receptacle A lighted by an electriclamp P and cause chlorine gas to bubble therein until troduced is of theorder of 1 kg. During this operation the solution is kept at atemperature chloride per he. is obtained. After elimination of thebenzene and chlorobenzenes'by evaporation with water vapour, theremaining solid product has a melting point of the order of 70 C.

Meanwhile there has been withdrawn from the fllter Fin the course ofchlorination 1300 gr. of a crystalline mass impregnated with motherliquor, which mass being washed with benzene in L and er. of a product.melting at 150 C. and formed chiefly ofa benzene hexachloride. Thebenzenic solution which has served for washing the precipitate iscollected at D and used as starting material for further chlorination.

I claim:

1. A process of producing a concentrated solution of y benzenehexachloridein benzene, comprising introducing into a vat containingbenzene a quantity of chlorine gas sufficient to obtain a solutionapproximately saturated with 'y isomer, the reaction being carried outunder the influence of light, continuously liquid from said vat to acrystallizer and back into said vat, cooling the liquid in saidcrystallizer, separating the crystals of the a and p isothe totalquantity incirculating the reacting l mers in said crystallizer, Washingsaid crystals with fresh benzene, and using the washing solution asstarting material for further chlorination, the liquid at the end of thechlorination comprising a concentrated solution approximately saturatedwith 'y isomer.

2. A process of producing a concentrated solution of 'y benzenehxachloride in benzene, comg the influence of light to efl'ectsubstantial chlo- 1 prising reacting chlorine gas with benzene under theinfluence of light, forming a benzenic solution l accuses of benzenehexachloride isomers at a concentration corresponding to saturation witha and 19 isomers at the temperature of reaction, cooling said solutionthereby causin crystals of the a and p isomers to precipitate,separating said crystals from said solution, raising thetempera-- tureof the resultin solution and proceeding with the chlorination thereofuntil a high concentration in 'y isomer is reached.

3. A process of producing a concentrated solution of benzenehexachloride in benzene, com

prising reacting chlorine gas with benzene in a chamber under theinfluence of light, causing the resulting solution to circulate out ofand into said chamber, controllin temperature conditions inside andoutside of said chamber to cause crystals of the c. and p isomers ofbenzene to precipitate outside of said chamber, separating said crystalsoutside of said chamber, proceeding with the chlorination in saidchamber until the circulating solution is approximately saturated with'y isomer and withdrawing at least a part of the solution approximatelysaturated with 'y isomer.

5. In a process of producing a concentrated solution of 'y benzenehexaehloride in benzen as claimed in claim 4, washing the crystals ofthe a and ,3 isomers with benzene and feeding the washing solution tosaid chamber.

6. A process of producing a concentrated solution of 'y' benzenehexachloride comprising gradually introducing into a reactor-bothbenzene and a quantity of chlorine gas sufficient to obtain a solutionapproximately saturatedwith "y isomer, carrying out the chlorination insaid reactor under the influence or light, continuously circulating thereacting liquid from said reactor to a crystahizer and heel: into saidreactor, keeping said crystallizer at a temperature'beiow the tem--perature in said reactor, thereby causing crystals of the a and pisomers to precipitate, separating said crystals from the circulatingliquid, washing said crystals with fresh benzene, introducing thewashing solution into the reactor so that it forms at least part of thebenzene required for chlorination, controlling the chlorination so thatthe circulating liquid remains saturated with each of the a, ,c and 'yisomers at the temperature of the crystallizer', and continuouslywithdrawing a portion of the circulating liquid at a rate correspondingto the rate ofchlorination.

7. A method of forming and separating a concentration of 'y benzenehexachloride isomer comrination thereof, continuously withdrawing fromthe reactor a portion of the benzene hexachloride solution in benzene ata rate substantially corresponding to the-rate of chlorination andcooling the solution .in a crystallizer whereby crystals of alpha andbeta isomers separate, recyclingthe mother liquor irom the crystailizerto the reactor continuously until the mother liquor is approximatelysaturated with the gamma isomer,

withdrawing a portion of the gamma saturated mother liquor from thesystem and replacing the same with unreacted benzene and recycling thediluted mother liquor to the reactor.

8. The method as defined in claim 7 wherein the separated crystals arewashed with benzene and the wash liquor thereof is used as a source ofsupply of unreacted benzene to the reactor.

MAX GONZE.

- REFERENCES CITED The following references are of record in the file ofthis patent:

6 UNITED STATES PATENTS Number Name v Date 2,218,148 Hardie Oct. 15,1940 2,438,900 Cooke et a1. Apr. 8, 1948 FOREIGN PATENTS Number CountryDate 504,569 Great Britain Apr. 26, 1939 573,689 Great Britain Dec. 3,1945 OTHER REFERENCES

1. A PROCESS OF PRODUCING A CONCENTRATED SOLUTION OF $ BENZENEHEXACHLORIDE IN BENZENE, COMPRISING INTRODUCING INTO A VAT CONTAININGBENZENE A QUANTITY OF CHLORINE GAS SUFFICIENT TO OBTAIN A SOLUTIONAPPROXIMATELY SATURATED WITH $ ISOMER, THE REACTION BEING CARRIED OUTUNDER THE INFLUENCEOF LIGHT, CONTINUOUSLY CIRCULATING THE REACTINGLIQUID FROM SAID VAT TO A CRYSTALLIZER AND BACK INTO SAID VAT, COOLINGTHE LIQUID IN SAID CRYSTALLIZER, SEPARATING THE CRYSTALS OF THE A AND BISOMERS IN SAID CRYSTALLIZER, WASHING SAID CRYSTALS WITH FRESH BENZENE,AND USING THE WASHING SOLUTION AS STARTING MATERIAL FOR FURTHERCHLORINATION, THE LIQUID AT THE END OF THE CHLORINATION COMPRISING ACONCENTRATED SOLUTION APPROXIMATELY SATURATED WITH $ ISOMER.